mapper: update lock's return values

Require mapper to return more information when locking a buffer.
Opaque vendor formats make it difficult to manipulate a locked
buffer. The pointer to the buffer's data is always at the top
left hand corner of the buffer. It can be impossible to know
where the locked region begins.

The mapper now must return the bytes per pixel and bytes
per stride of a locked buffer when the values are consistent
and known.

Bug: 120493579
Test: vts
Change-Id: Id0921f191f1e388d4950ecef73acab6a34010dc4